Known coater die component methods of manufacture call for an 8 to 16 microinch finish on all of the surfaces. The surfaces are ground to this finish. The surface also should be unbroken with deburred edges at the die lips. The die components are ground along their length to minimize formation of a "sawtooth" pattern on the coating edges which would lead to catastrophic levels of streaking. The die component edges can be deburred by hand if necessary, possibly with a non-woven material or a suitable sharpening stone. There is no further micropolishing. The die component edges are ground to the same finish as the rest of the component. This does not always lead to sufficiently polished surfaces and causes streaking in the coating of products. Even freshly ground dies made by the best known methods can still produce streaks.
Typically, the surfaces of the die are ground using a grind wheel to surface grind each surface of each die component which is contacted by coating fluid during coating. Known grinding of mater dies is shown in FIGS. 1A and 1B. These Figures show using a grinding wheel 10 to grind two surfaces 12, 14 of the three surfaces of the die component 18 edge. (The third surface 16 also will be ground.) The simplest way to make the die parts is to do the final surface grinding along the die length. This method, however, leads to formation of a burr on the die edges that must be removed, and leads to an uneven edge morphology.